| 1. |
- Ayele, Getnet Tadesse, et al.
(författare)
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An extended energy hub approach for load flow analysis of highly coupled district energy networks: Illustration with electricity and heating
- 2018
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Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 212, s. 850-867
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Tidskriftsartikel (refereegranskat)abstract
- Energy systems at district/urban level are getting more complex and diversified from time to time. Different energy carriers are coupled each other to meet various types of energy demands. The conventional way of analyzing energy networks independently does not reflect the true nature of the coupled networks. One of such a promising coupled multi-carrier energy system (MCES) is the combination of district heating and electricity networks. The coupling between these two networks is increasing due to the integration of co– and poly-generation technologies at the distribution networks. Recent literatures tried to address a load flow analysis for lightly coupled networks by formulating case-specific load flow models. This paper presents a more general and flexible tool developed using Matlab® which can be used to conduct the load flow analysis of highly coupled electricity and heating networks. An energy hub concept is extended further to formulate a general model in which local generations and detailed network parameters of MCES can be taken into account. Coupled heating and electricity networks are modeled in detail for illustration. The flexibility and generality of the model are then tested by considering case studies with different network topologies (tree and meshed). A comparison is also made with a model used in recent literature. The results show that the proposed model is more accurate. The main contribution of this paper can be summarized by the following five points: (1) Coupling matrices are used to relate network power flow equations of different energy carriers; (2) Hybrid hydraulic head and pipe flow equations are used to develop the hydraulic model which can be applied for both types of tree and meshed heating networks with the possibility of pumping units; (3) A general thermal model that relates steady state temperature drops and mass flow rates, even during change of flow direction, is developed for the heating network; (4) The electricity network is modeled with the possibility of tap changing transformers; (5) The overall system of equations are solved as a single problem using Newton-Raphson iterative method.
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| 2. |
- Ayele, Getnet Tadesse, 1987-, et al.
(författare)
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Electrified district heating networks : a thermo-economic optimisation based on exergy and energy analyses
- 2021
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Ingår i: International Journal of Exergy. - : Inderscience Publishers. - 1742-8297 .- 1742-8300. ; 35:1, s. 100-131
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a thermo-economic optimisation of an electrified district heating network consisting of wind power plant, gas-fired combined heat and power plant and heat pumps. The load flow problem of the resulting multi-energy system is formulated by considering all physical and operating parameters in both of the electricity and heat distribution networks. First, energy and exergy analyses are applied to identify and isolate lossy branches of a meshed heating network. This is followed by the optimal placement of heat pumps. Finally, supply and return temperatures are optimised. Particle swarm optimisation technique is implemented in order to find the best place of heat pumps, their economical dispatch and optimal temperature profile of the district heating network. Results show that up to 59.12% of the distribution heat loss and 9.37% of the operating cost can be saved by following a step-by-step methodology discussed in this paper.
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| 3. |
- Ayele, Getnet Tadesse, et al.
(författare)
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Exergy analysis and thermo-economic optimization of a district heating network with solar-photovoltaic and heat pumps
- 2019
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Ingår i: ECOS 2019 - Proceedings of the 32nd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems. - : Institute of Thermal Technology. - 9788361506515 ; , s. 1947-1959
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Konferensbidrag (refereegranskat)abstract
- Electrification of district heating networks, especially using heat pumps, is widely recommended in literature. Installing heat pumps affects both electricity and heating networks. Due to lack of suitable modelling tools, size optimization of heat pumps in the heating network with the full consideration of the electric distribution network is not well addressed in literature. This paper presents an optimization of a district heating network consisting of solar photovoltaic and heat pumps with the consideration of the detail parameters of heating and electric distribution networks. An extended energy hub approach is used to model the energy system. Exergy and energy analyses are applied to identify and isolate lossy branches in a meshed heating network. Both methods resulted into the same reduced topology. Particle swarm optimization is then applied on the reduced topology in order to find out the most economical temperature profiles and size of distributed heat pumps. The thermo-economic results are found to be highly influenced by the heat demand distribution, the power loss in both electric and heat distribution network, the cost of generation, the temperature limits and the coupling effect of the heat pumps.
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| 4. |
- Ayele, Getnet Tadesse, 1987-
(författare)
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Exploiting the Synergies from Coupled Electricity and Heat Distribution Networks : Modelling, simulation and optimization based on an extended energy hub approach
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent literature shows that there is a significant potential of decarbonisation and efficiency improvement that can be achieved through the synergy from multi-energy systems (MESs). Coupling technologies, such as co-generation plants, heat pumps and thermal storages are widely recommended as means of unlocking additional flexibility and increasing the penetration of renewables in the heating and electricity sectors. In view of that, the size and number of coupling technologies, such as combined heat and power plants and heat pumps (HPs), being installed in the heat distribution networks are increasing. As these technologies are exclusively managed by the district heating network operators, their operation sometimes becomes suboptimal from the electricity network point of view, and they (in particular large HPs) may cause overloading of the low voltage electricity distribution networks.Integrated simulation and optimisation models are required to exploit the synergies effectively without compromising the constituent distribution networks of MES. Such models are not yet well developed. The conventional single-energy-carrier simulation tools are not capable of capturing key operating parameters of the multi-carrier distribution networks either.A novel methodology for simulation and optimisation of MES is developed in this thesis based on an Extended Energy Hub (EEH) approach. The general framework is first developed in modular form so that it can be easily adapted for any type of multi-carrier energy networks. The framework is then used to develop the details of an integrated load flow model governing coupled heating and electricity distribution networks. Various load flow case studies with radial and meshed topologies are considered for demonstration and numerical validation of the proposed model.The load flow model is further combined with a particle swarm optimisation algorithm in order to conduct integrated optimal power flow studies. Its contribution to the state of art is demonstrated by studying the optimal placement of coupling technologies, such as HPs and boilers in coupled heating and electricity distribution networks. The capacity of the model is further illustrated by exploiting the synergies using HPs together with thermal storage in the presence of intermittent renewables and variable electricity price signal.It is shown that the EEH-based simulation and optimisation methodologies proposed in this thesis are very effective, flexible and easily scalable in capturing the key operating parameters of integrated electricity and district heating networks. The models can be used as a platform for further studies on integration of smart grids and smart thermal networks.
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| 5. |
- Ayele, Getnet Tadesse, et al.
(författare)
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Optimal heat and electric power flows in the presence of intermittent renewable source, heat storage and variable grid electricity tariff
- 2021
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904 .- 1879-2227. ; 243
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Tidskriftsartikel (refereegranskat)abstract
- To decarbonize and increase the flexibility in the heating and electricity sectors, large heat pumps, combined heat and power plants, renewables and storage technologies are increasingly being installed. This results in a tighter coupling between the electricity and heat distribution networks. Hence, the two networks need to be operated in an integrated way so that their synergies can be exploited. The main challenge in that regard is the lack of suitable tools that can capture the detailed operating parameters of both networks simultaneously. This paper proposes a population-based optimal power flow model for integrated heat and electricity distribution networks. An extended energy hub approach is used to model the components of the integrated energy system in a modular form. Active and reactive power balances, heat power balance and optimal management of storage technologies in the presence of intermittent renewables and variable tariffs are considered. The proposed method is then tested using a case study of highly coupled electricity and heat distribution networks consisting of a heat pump, a gas boiler, a combined heat and power plant, a wind turbine and a thermal storage together with a variable electricity tariff. It is found that above 97% of the surplus production from the wind power plant is effectively used in the system and 10.35% of the heat demand is effectively shifted from the peak hours to the cheap-electricity hours. The results show that the proposed method can be used as a decision support tool that can be used for the optimal integration of heat and electricity distribution networks. It also maximizes the synergy that can be captured from the multi-energy systems in general and from the heat and electricity distribution networks in particular.
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| 6. |
- Ayele, Getnet Tadesse, et al.
(författare)
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Optimal placement and sizing of heat pumps and heat only boilers in a coupled electricity and heating networks
- 2019
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Ingår i: Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0360-5442 .- 1873-6785. ; 182, s. 122-134
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Tidskriftsartikel (refereegranskat)abstract
- Multi-energy systems are reported to have a better environmental and economic performance relative to the conventional, single-carrier, energy systems. Electrification of district heating networks using heat pumps and combined heat and power technologies is one such example. Due to lack of suitable modelling tools, however, the sizing and optimal placement of heat pumps is always done only from the heating network point of view which sometimes compromises the electricity network. This paper proposes an integrated optimization algorithm to overcome such limitation. A load flow model based on an extended energy hub approach is combined with a nested particle swarm optimization algorithm. A waste to energy combined heat and power plant, heat pumps (HPs), heat only boiler (HOB), solar photovoltaic, wind turbines and imports from the neighborhood grids are considered in the case studies. The results show that optimal placement and sizing of HPs and a HOB using the proposed methodology avoids an unacceptable voltage profiles and overloading of the electricity distribution network, which could arise while optimizing only from the heating network point of view. It also shows that up to 41.2% of the electric loss and 5% of the overall operating cost could be saved.
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| 7. |
- Ayele, Getnet Tadesse, et al.
(författare)
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Pseudo-dynamic simulation on a district energy system made of coupling technologies
- 2018
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Ingår i: Proceedings of ECOS 2018 - the 31<sup>st</sup> International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems June 17-22, 2018, Guimarães, PORTUGAL. - : University of Minho. - 9789729959646
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Konferensbidrag (refereegranskat)abstract
- As part of an effort towards the future smart energy system, integration of different distributed generation technologies is proposed in literature. These technologies include heat pumps, gas boilers, combined heat and power (CHP) plants, solar photo-voltaic (PV) and so on. Some of these technologies couple different energy carriers in which case the independent analysis of each network could lead to unrealistic results. Optimization of heat pumps and CHP plants in coupled electricity and heating network, for example, needs consideration of both networks’ parameters in order to get results that are optimal in both networks. The first step in such optimization process is to have a load flow model (as an equality constraint) for the two coupled networks. Even though many researchers tried to address optimization of energy mixes at a district level, they did not consider the details of network parameters. Too little has been done to investigate the effect of different distributed generation technologies on the operational parameters of different energy networks. This paper deals with a pseudo-dynamic simulation of a district energy system that consists of coupled electricity and heating networks. The details of transmission line and pipe parameters together with the coupling devices are modelled using an extended energy hub approach. A network of six energy hubs with different distributed generation technologies such as heat pump, gas boiler, CHP and Solar PV is considered in the simulation. Time series data for demands and generations at different hubs are used on hourly basis. The CHP and heat pumps are scheduled to operate in certain period of the year while the PV output follows the annual solar radiation. Annual pseudo-dynamic load flow simulation is done to see how the operational parameters and power losses in the network vary with hourly changes in demands, generations and loading of coupling technologies.
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